Conventionally, a swashplate type compressor is used in systems such as an air conditioning system of an automobile. According to a known swashplate type compressor, the transmission of motive power is carried out, as a swashplate and a piston reciprocate, thereby suctioning, compressing and discharging the gas. The swashplate is usually composed of aluminum or iron alloy and shoes, which make slideable contact with the swashplate when it rotates, are composed of iron or copper alloys. The metal on metal contact at the shoe and swashplate interface requires special precautions to be taken in order to prevent undue wear and possible seizure of the shoe with the swashplate.
Lubrication in the swashplate type of compressors is critical to their reliability, especially at the swashplate sliding surface. During the service life of the compressors, the swashplate surface may encounter low lubricant supply. Sometimes a compressor may even run with no lubricant at all for a short period, which can result in swashplate damage or, in extreme situations due to the generation of significant heat, compressor seizure. A good countermeasure to this problem has been to apply lubricious coatings on swashplates.
For example, U.S. Pat. No. 5,056,417 treats a swashplate body with a surface coating layer made of tin and at least one metal selected from the group consisting of copper, nickel, zinc, lead and indium. In patent application U.S. Ser. No. 08/050,215, filed Mar. 30, 1998 and commonly assigned herewith, a tin/cobalt coating is disclosed which has improved wear resistance and also excellent adhesion to the swashplate.
Polymer based coatings have also been suggested for coating aluminum swashplates. U.S. Pat. No. 5,655,432 treats a swashplate with a coating of a mixture of cross-linked polyfluoro-elastomer bonded directly to the aluminum, a lubricious additive and a load bearing additive like boron carbide. The part is masked to apply the coating in only certain areas. Sho 58-129646 discloses a swashplate coated with a solid lubricant such as boron nitride, fluorine resin solidified with resin. It also discloses coating with soft metals like tin and lead. Polymer based coating, while providing excellent friction reduction and seizure resistance at dry condition, have less than desirable wear resistance (durability) due to the physical characteristics of the polymers. That is, they are soft compared to the counterparts they contact, normally ferrous metals, and become even softer at higher temperatures. Because of this, polymer coatings have not found commercial acceptance as lubricious coatings for aluminum swashplates.
The present invention overcomes the deficiencies of other swashplate coatings by providing a coating with excellent wear resistance, low sliding friction and additionally good thermal conductivity.